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Gaining control

New plant control technology has helped Birse Civils lay 3.5km of dual carriageway in Suffolk with great accuracy.

 The A14 Haughley New Street to Stowmarket improvement, a Highways Agency project involving 3.5km of dual carriageway and around 275,000m3 of earth moving, has opened ahead of schedule.    

New plant technology has played a major role.    

Birse Civils won the contract, which was awarded under the Highways Agency’s Early Contractor Involvement (ECI) initiative. As part of this initiative, locally based Lancaster Earthmoving was involved from the earliest stages, bringing its three years of experience in machine control to the mix. Machine control technology helps contractors position plant and place machinery to a very high degree of accuracy.    

“The construction industry can be staid and sometimes slow to utilise new technologies and methods,” says Birse project manager David Huckstep. “The Highways Agency has around 15 major road projects worth over £10M under construction and less than a third of those have utilised machine control so there is a low take up in the industry.”    

The construction industry can be staid and sometimes slow to utilise new technologies and methods

David Huckstep, Birse

Lancaster supplied two types of systems to the site – Trimble’s GCS900 Grade Control System for dozers using dual GPS on Komatsu D61 and CAT D6N Dozers and Trimble’s GCS900 system for graders utilising a Trimble Universal Total Station (UTS) on a CAT140G Motorgrader. The dozer systems use GPS technology to accurately position an excavator blade in real-time with transmitted corrections coming from a Trimble SPS851 Base Station established by Lancaster on the works cabin roof. Positioning sensors are used to compute the exact position of a blade many times per second. The on-board computer uses this information and compares it to the design elevation to compute cut or fill to grade. The information is displayed on an in-cab screen.    In the site office, information provided by scheme designer Mouchel is converted to the correct format and then loaded onto a memory card for transfer to the cab-based control box. Design changes can be quickly and easily distributed the same way.    

“Initially we were very cautious and to ensure everyone had confidence in machine control we used traditional setting-out methods as well,” says Birse section engineer Dave Annan.    

“As confidence grew, the setting-out for the bulk earthworks was reduced and almost completely taken away for the final trim. A comparison of results showed that the blade was producing a consistent accuracy of +/-30mm and the grader was typically producing +/-5mm – much better results than we were achieving using traditional methods when each stage of the process can induce an error. Now it’s definitely a case of ‘right first time’ and rework has been minimal, freeing up my time for checking and data handling.”    

While the Highways Agency normally requires a sub-base tolerance of +10/-30mm, Birse managed to cut this to just +5/-5mm by carrying out the final grade with Trimble’s GCS900 system for graders using a Trimble UTS on a CAT140G Motorgrader. The UTS uses active target technology to reliably lock onto and track the target on the grader’s blade. Its high up-date rate, low latency and synchronized angles and distance measurements capabilities make it ideal for blade guidance to between 2mm and 5mm accuracy. “If the foundations are right, it will follow you through to the top, and that certainly proved to be the case when it came to the blacktop,” says Annan.    

“The end result was also aided by the fact that the construction of the base course and wearing course layers was conducted using a sonic averaging beam on the paver to sustain and improve rideability. The Trimble machine provided us with continuous grade control so when it came to the blacktop, we agreed a thickness and Lafarge, our blacktop contractor, just let the paving machine run instead of the operatives constantly making manual adjustments.”      

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